HttpClient and stream issues

System.Net.Http.StreamContent and System.IO.FileStream are instantiated but not disposed.

Add the code to invoke Dispose like you did in finally block.

try{    # enclose the program}finally{    if($null -ne $streamContent)    {        $streamContent.Dispose()    }    if($null -ne $packageFileStream)    {        $packageFileStream.Dispose()    }}

That exception is clearly threading-related.

Your method calls use async method calls, but not correctly:

.ReadAsStringAsync().GetAwaiter().GetResult()

just blocks the current thread while waiting for another: it actually takes up an additional thread.

So, because you're a) not using threading in a useful fashion and b) getting an exception for your efforts, I suggest you take anywhere in your code which uses that construct and replace it with a normal method call.

Edit:

Threading issues aside, you could try

$content.Add($streamContent)$content.LoadIntoBufferAsync().GetAwaiter().GetResult()

to force the content stream to load prior to the next async post operation.

Be careful - this NotSupportedException can mask a different error, such as an authorization problem (e.g. incorrect credentials passed in the NetworkCredential object).

I found this out by running Fiddler and watching the responses.